I'm thinking of all the local, excellent bands of the 70's and 80's in the folk genre(s), who self-produced a cassette or two to sell at local gigs and local festivals. Not big enough or well-known beyond their local areas to attract a label to press an LP. And probably didn't have the time, given they all had day jobs.   There was no internet, and certainly no youtube, myspace, etc.

Tapes wear out. Musicians themselves move on, grow, transition. And no one thought to appoint an archivist. Contact some of the musicians one can locate now who were in those earlier bands, and many of them don't know what became of the masters for those earlier cassette recordings of earlier bands they were in.

From my own local experience and history -Critten Hollow String Band. All of them are still around, but the early music they produced on cassette is not available. Can't order the cassettes and those early productions are also not available digitally or as a CD. Ditto the Bing Brothers, "Just For the Sake of It." Pomegranate Rose, Trapezoid, Back Porch String Band. (some of my own local examples.)

A lost history, imo.